| From: | Gregory Stark <stark(at)enterprisedb(dot)com> |
|---|---|
| To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>, "Bruce Momjian" <bruce(at)momjian(dot)us>, "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Florian Pflug" <fgp(dot)phlo(dot)org(at)gmail(dot)com>, "PostgreSQL-patches" <pgsql-patches(at)postgresql(dot)org> |
| Subject: | Re: HOT patch - version 15 |
| Date: | 2007-09-11 07:12:01 |
| Message-ID: | 87tzq1llq6.fsf@oxford.xeocode.com |
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| Lists: | pgsql-patches |
"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> What it sounds is utterly unsafe. You can get away with not WAL-logging
> individual bit flips (that is, hint-bit-setting) because either state of
> the page is valid. If I read this proposal correctly it is to change
> t_ctid without WAL-logging, which means that a partial page write (torn
> page syndrome) could leave the page undetectably corrupted --- t_ctid
> is 6 bytes and could easily cross a hardware sector boundary.
Well we would never be overwriting the blockid, only the posid which is 2
bytes. And the ctid (and posid) should always be 4-byte aligned. So actually
it would never cross a hardware sector boundary.
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
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